Final answer:
Cells produce different types of proteins because they express different genes that code for specific proteins.
Step-by-step explanation:
Cells can produce different types of proteins because they express different genes that code for specific proteins. Each cell type needs a different set of proteins to perform its function. Therefore, only a small subset of proteins is expressed in a cell. The expression of specific genes is a highly regulated process, ensuring the proper expression in the proper cell at the proper time.